1. Field of the Invention
The present invention relates to the technical field of semiconductor electronics and particularly to the technical partial field of high-frequency MOS transistors.
2. Description of the Prior Art
High-frequency switches have the task to pass or block high-frequency signals. In the passing case, the same should be characterized by an ohmic resistance, which is as small as possible, and in the blocking case, by a constant capacity, which is as small as possible. They can be realized by different types of switching elements. In silicon technology, high-frequency switches are often realized with bipolar or MOS transistors (MOS=metal oxide semiconductor). However, in the off-state, they require a base or substrate voltage, respectively, as high as the high-frequency amplitude which is to be blocked. Thereby, the switchable power of the available bias voltage is limited. This means that in the case of a silicon MOS transistor, the passing and blocking case can be easily realized when the high-frequency signals to be switched are limited to a low amplitude of these high-frequency signals. The passing case is then obtained for an n channel MOS transistor by applying a positive gate source voltage, wherein the same has a small resistance. With proper transistor dimensioning, the control voltage can remain below 3 volt and thus be within the operating voltage used in mobile radio systems. The allowed current amplitude can be set via the width/length ratio of the channel. The blocking case occurs by changing the polarity, i.e. a positive source gate voltage disconnects the current and the drain gate capacity remains as load impedance. The starting voltage should be around 0 volt. The maximum voltage amplitude occurs through the secondary condition that the drain bulk diode must not be polarized in forward direction, at maximum 3.5 volt, when the maximum bias voltage is equal to the supply voltage of 3 volt and the diode can still be operated with 0.5 volt in forward direction.
In order to able to switch higher powers by high-frequency switches, conventionally, these high-frequency switches are realized outside the RF-Ics (RF-ICs=radio frequency integrated circuit) in the form of pin diodes or GaAs transistor switches. The same can be operated with low or without bias voltage, respectively. However, the higher costs are disadvantageous, which are incurred by the additional parts and which make an integration with a unitary semiconductor technology, such as a pure silicon technology, more difficult.
The maximum control of a high-frequency switching transistor, such as a conventional MOS transistor is often determined by its parasitic lateral bipolar transistor, which should not come into the passing region, when the same is realized by a contiguous silicon substrate. A basic measure for making the parasitic bipolar transistor resistant to large signals, has already been described in EP 03028319.6, wherein this patent application relates to the optimization of parasitic bipolar transistors, wherein, however, these transistors are significantly lossy when high powers are to be switched.
WO 03/032431 A3 shows a circuit and a method for switching high-frequency signals, wherein the high-frequency circuit is produced in a silicon on insulator technology. The high-frequency circuit comprises pairs of switching and shunt transistor groups, which are used to alternately couple high-frequency input signals to a common high-frequency node. The switching and shunt transistor groups comprise one or several MOSFET transistors, which are connected in a “stacked” or series configuration. By stacking transistor groups, the breakdown voltage across the switching transistors connected in series is increased. A fully integrated high-frequency switch is described, which comprises a digital control logic in a negative voltage generator, which is integrated with the high-frequency switching elements. In one embodiment of the WO 03/032431 A3, the fully integrated high-frequency switch comprises an integrated oscillator, a charge pump circuit, a level shifter, voltage divider switching circuits and a high-frequency buffer circuit.
U.S. Pat. No. 5,777,530 comprises a circuit attenuator, which comprises a first terminal connected to an antenna, a second terminal connected to a transmitter, and a third terminal connected to a receiver, whereby switching of a first state and a second state becomes possible. In the first state, the first terminal is connected to a second terminal, the first terminal is electrically isolated from the third terminal, the third terminal is connected to ground and the circuit attenuator is electrically controllable to vary an attenuation amount between the first terminal and the second terminal and at the same time to maintain a relationship that an impedance Z1 seen from the first terminal is essentially equal to a second impedance Z2 seen from the second terminal. In the second state, the first terminal is connected to the third terminal, the first terminal is electrically isolated from the second terminal and the second terminal is connected to ground and the circuit attenuator is electrically controllable to vary an attenuation amount between the first and the third terminal while a relationship is maintained that the impedance Z1 seen from the first terminal is essentially equal to an impedance Z3 seen from the third terminal.
WO 9946859 discloses a microwave circuitry with one or several semiconductor switching elements, characterized by at least one semiconductor switching element being controlled or switched, respectively, by changing the drain and source potential. These circuits can be used in mobile phones or mobile transceivers.
US-2003/0090313 A1 shows a high-frequency circuit and a method for switching high-frequency signals. The high-frequency circuit is produced in a silicon on isolator technology (SOI). The high-frequency circuit comprises pairs of switching and shunt transistor groups, which are used to alternately couple high-frequency signals to a common high-frequency node. The switching and shunt transistor grouping pairs are controlled by a circuit control voltage and it's inverse. The circuit and shunt transistor groups comprise one or several MOSFET transistors, which are connected in a “stacked” or series circuit.
U.S. Pat. No. 5,812,939 comprises a circuit-semiconductor integrated circuit, wherein a switch for a high-frequency signal is formed by four field effect transistors stages, which are connected in series to the first to fourth signal path, which is arranged in a ring shape, and two connected field effect transistors stages, which are in a shunt position with regard to the signal path, so that two signal paths are disposed between two opposite field effect stages.
In order to eliminate problems of parasitic lateral bipolar transistors, which occur on a contiguous silicon substrate, the high-frequency power switch can also be generated in a gallium arsenide technology or on a substrate consisting of a thin silicon layer of a thick sapphire substrate, so-called silicon on sapphire (SOS). Both technologies are more expensive than Si technology.
Additionally, when using gallium arsenide technology or SOS technology, high-frequency power switches can only be integrated sufficiently compact in a limited way in an integrated circuit.